The following oxygen reduction reaction is a cathode reaction in a H2/O2 fuel battery, brine electrolysis, and the like, and plays an important role in an electrochemical energy conversion device and the like.O2+4H++4e−→2H2O
The following oxygen evolution reaction which is a reverse reaction of the oxygen reduction reaction is an anode reaction in water electrolysis and the like, and also plays an important role therein.2H2O→O2+4H++4e−
To promote the oxygen reduction reaction or the oxygen evolution reaction in various devices, noble metal such as platinum, ruthenium oxide, and iridium oxide has been widely and normally used as a catalyst.
However, these kinds of noble metal are rare and expensive, and the costs thereof are unstable. Therefore, using noble metal poses problems in view of saving natural resources, ensuring availability, lowering the cost, and the like.
In this regard, recently, as an oxygen reduction reaction catalyst, a carbon-based member doped with metal and nitrogen has been developed and has attracted attention as a promising catalyst altetive to noble metal. For example, non Patent Literature 1 discloses that a carbon-based crystal containing iron and nitrogen is prepared by heating a mixture of iron phthalocyanine and a phenolic resin at a heating temperature ranging from 700° C. to 900° C. for a heating time ranging from two to three hours under inert atmosphere, and that the carbon-based crystal functions as a catalyst promoting oxygen reduction. Besides, non Patent Literature 1 discloses that in a catalyst formation process, iron has also a catalytic function of promoting crystallization of the carbon-based crystal.
Non Patent Literature 2 discloses that a carbon-based crystal containing iron and nitrogen is obtained by preparing a mixture of graphene oxide, iron chloride, and graphitic carbon nitride (g-C3H4), chemically-reducing the graphene oxide of the mixture to graphene using a reducing agent, and then heating the resultant mixture at a heating temperature of 800° C. for a heating time of two hours under argon atmosphere. Besides, non Patent Literature 2 discloses that the carbon-based crystal functions as a catalyst for promoting oxygen reduction.
In order that such a catalyst shows sufficient catalytic activity, it is required to sufficiently increase the number of reaction active centers by sufficiently widening an area per sheet of graphene sheets, or to dope one graphene sheet with more amounts of iron and nitrogen, the graphene sheets composing of the carbon-based crystal. To achieve this, in the past, attempted have been methods of increasing the heating temperature under inert atmosphere for preparing the carbon-based crystal and of increasing the heating time.